"Hundreds of thousands have been displaced, thousands raped, hundreds of villages burnt to the ground and at least 1,000 civilians killed," Philip Alston, the United Nations' special rapporteur on extrajudicial executions, said in a statement. "In many areas, it is [Congolese soldiers] themselves who pose the greatest direct risk to security."

U.N. officials are scheduled to discuss the situation Friday.

Alston's statement followed a trip to the vast central African nation to investigate alleged state killings and other rights abuses. Much of his visit focused on the east, where by some estimates a 15-year-long conflict has killed more than 5 million people.

In the conflict's latest phase, the Congolese army has been trying to flush out Rwandan rebels who for years have lived by force among Congolese villagers. A U.N. peacekeeping mission is backing the operation, called Kimia II, by providing food and other logistical support. The United States has provided funding and diplomatic support.

But the operation raised alarm when it started in January. Human rights groups, aid workers and Congolese civilians repeatedly warned that it would prompt rebels to retaliate against villagers, and they questioned the wisdom of a mission carried out by underpaid, ill-trained Congolese soldiers.

Ten months later, Alston said, poor planning and coordination have led to "predictable and repeated killing." In one case, he said, Congolese soldiers shot and beat to death at least 50 civilians living among the rebels and abducted about 40 women, some of whom described being gang-raped. The rebels apparently retaliated by massacring at least 96 civilians in the village of Busurungi who were accused of collaborating with the army.

An epidemic of sexual violence has worsened, and such attacks "may be particularly vicious" when they are intended to punish villagers for allegedly backing the rebels or the army, Alston said.

"Women and girls -- including babies -- have been gang-raped, had guns, wood, sand or glue inserted into their bodies, and had their genitals mutilated," he said. "Some women have had fetuses ripped out of their wombs by perpetrators. Victims have, in fact, quite literally been raped to death."

Widespread impunity is at the root of much of the violence, particularly when it is carried out by the military, Alston said. He noted that a top Congolese army official said that only 15 percent of reported rapes had occurred and that "it was in the nature of women to be unfaithful."

Alston called for the indictment of five high-ranking army officials accused of war crimes, saying their presence in the army "only serves to mock human rights."

"No amount of sophisticated strategic rationalization should be permitted to obscure that fact," he said.